A variety of fixation devices for the reduction of bone or bone fragments or for spinal fixation are well known. Spinal fixation devices including intervertebral implants, spinal rods, and the like, are used to replace intervertebral discs, fuse or align adjacent vertebrae, and address other spinal issues. Long bone fixation devices commonly include both external and internal fixators that are attached to underlying bone. Spinal fixation devices and long bone fixation devices typically are affixed to underlying bone via one or more bone anchors.
For instance, a typical bone plate includes screw holes that accommodate bone screws which are drilled into underlying bone on opposing sides of a fracture to join bone segments together. A typical cervical spine implant can likewise include screw holes that accommodate screws which are drilled into adjacent vertebral bodies in order to fix the position of the implant. In certain applications it is desired to provide relatively small bone screws. For instance, spinal screws are having thread and head diameters less than 10 mm are commonly used. Bone screws of this size can become compromised when exposed to high torque/force that are applied when drilling, tapping, or otherwise inserting the anchor into underlying bone.
What is desirable is bone anchor configured to accept high torque/force without compromising the anchor's bending/shear strength.